Humans differ from other great apes in many ways, but one crucial difference is that our social worlds are vastly more co-operative than those of any other great ape. In my view, we now have a good conceptual model of the origins of human co-operation and it stability in the Pleistocene. But Pleistocene co-operation was co-operation amongst intimates and amongst equals. Around 10 thousand years ago, in the early Holocene, some humans abandoned foraging for farming, and over the next few thousand years, for many, the economic base of human life changed, and so did the social world. It become larger; more complex; less equal. Even so, collective action problems continued to be solved: indeed, the first large scale public works were the products of these complex, but pre-state societies. This second great transition in human social life poses three questions: (i) why did humans abandon foraging for farming? (ii) why did farming lead to (or correlate with) the origin of complex societies? (iii) how and why did the social contract survive this transition? We have good answers to none of these questions, but the third has scarcely be noticed as a question.